1. Field of the Invention
The present application is for a lamp for detecting leaks in commercial and industrial air-conditioning and refrigeration systems and other liquid recirculating systems such as those employing engine oil, transmission fluid and hydraulic fluid. The lamp uses a light-emitting diode (LED) as a light source to detect fluorescent dyes that have been added to the air-conditioning or refrigeration system.
2. Description of the Related Art
Leak detection, materials detection and qualitative non-destructive testing are well suited to techniques employing fluorescence detection. These techniques rely upon the unique physical property of various materials to fluoresce when excited by certain wavelengths of visible or ultraviolet (UV) light.
It is a well-known phenomenon that electromagnetic energy within the near ultraviolet spectrum of approximately 315 to 400 nanometer wavelengths produces fluorescence in certain materials, e.g., fluorescent dyes. These fluorescent materials absorb radiated energy at the near UV wavelengths and re-radiate or emit it at a longer wavelength in the visible spectrum. Thus, when fluorescent material absorbs electromagnetic energy in a specific excitation frequency band in a specific wavelength range, the material can emit electromagnetic energy in a characteristic fluorescent emission frequency band within the visible light spectrum. This phenomenon has enabled inspection and detection techniques in which fluorescent dyes, inks or pigments are illuminated by lamps selectively filtered to emit only ultraviolet (invisible to the human eye) and then re-radiate with a high luminescence in the visible spectrum. Some newer fluorescent dyes respond well to higher wavelengths of light in the visible violet and blue range in addition to the invisible UV range.
For example, the slow leakage of refrigerant from an air conditioning system is difficult to locate by any other means. The reason for the difficulty is because the refrigerant escapes as an invisible gas at such a low rate and rapid diffusion that the concentration of refrigerant in air near the leak site is difficult to differentiate from that surrounding any other location along the system circulation lines. However, by adding into the circulating system a small amount of fluorescent dye that is soluble in the refrigerant, the dye is carried out of the system with the refrigerant and glows brightly at the leak site when the area is swept with a UV lamp.
A similar procedure can be used to locate leaks of other fluids, such as lubricants, oils, fuels, heat transfer fluids or hydraulic fluids. Other UV inspection techniques use fluorescent dyes or paint to detect fissures or stress cracks in structural members.
Conventional inspection lamps employ high intensity light sources (incandescent bulbs) operating at high temperatures to generate a sufficient photon flux for detection applications and utilize filters to absorb the undesirable wavelengths. These bulbs give off light owing to their temperature (incandescence). The power of the lamps is very high in wattage and therefore the lamp produces heat. A black light filter can be used but the filter is very restrictive and allows only UV wavelengths to be transmitted while all of the remaining wavelengths are absorbed. These filters typically have a transmission efficiency of 50-70% for the UV wavelengths (320-380 nm). To compensate for the limited transmission efficiency, the power of the lamps is very high in wattage and therefore heat producing. These lamps are usually 20-150 watts. Consequently, the life expectancy of the bulb is limited.
The fluorescent dyes used in this system typically have maximum excitation in the range of 320-380 nm. Some newer dyes respond well to higher wavelengths of light in the visible violet and blue range in addition to the invisible UV range (340-440 nm). With these dyes, improved photographic-type blue filters are used with smaller, low wattage lamps. These blue filters work well in lamps of 50 watts or less. At 50 watts, the lamps do not produce as much heat and although the blue filter allows some visible light to be transmitted, the dyes are still acceptably excited. In most cases, the lamps using these blue filters are also sold with special glasses (blue blocker glasses) that block the visible blue spectrum light transmitted through the blue filters. These glasses assist the operator in finding the leaks and seeing the dye reaction to UV, blue and violet light. In addition, these blue filters are much more prone to temperature damage and cracking than the black light filters. However, the transmission efficiency is greater by about 10% as compared to that for the black light filters. Also, the blue filters and the blue blocker glasses make the dye more visible to the technician.
Newer improved filters have been developed by applying a dielectric coating, that does not effect the visible and lower spectrum of light transmission, to a piece of glass. Such filters are referred to as dielectric or dichroic filters. These terms are interchangeable. Dielectric refers to the process used, and dichroic is the type of coating applied, also known as thin-film coating. For example, dichroic filters with a dielectric coating have been developed in the entertainment industry and have high levels of transmission. The dichroic filter with a dielectric coating allows UV, blue and IR wavelengths to be transmitted while most visible wavelengths are blocked. Thus, this type of filter does not absorb the IR heat and has a transmission efficiency of over 90% for the desired wavelengths. These advantages allow users to reduce the size and wattage of the detection lamps.
Luminescence, on the other hand, is the result of electronic excitation of a material. The light-emitting diode (LED) is a p-n junction in which an applied voltage yields a flow of current, and the recombination of the carriers injected across the junction results in the emission of light. The process involved here is in effect electroluminescence. The ratio of the number of emitted photons to the number of electrons crossing the p-n junction is the quantum efficiency. LED emission is generally in the visible part of the spectrum with wavelengths from 400 nm to 700 nm or in the near infrared with wavelengths between 700 and 2000 nm.
Red, yellow and green light-emitting diodes are known. More than 20 billion LEDs are produced each year. Visible LEDs are used as numeric displays or indicator lamps and are sufficiently bright that a row of red LEDs are used in an automobile spoiler to replace the conventional rear-window brake light. Infrared LEDs are employed in optoisolators, in television remote controls, and as sources in optical communication systems. The applied voltage is near 2.0 volts. The current depends on the application and ranges from a few milliamperes to several hundred milliamperes. Thus, LEDs function with low power drain, at reduced temperatures and have an extremely long life expectancy, e.g., five to ten years or more, as compared to incandescent bulbs.
The present application reveals a lamp for detecting fluorescent dyes in an air-conditioning or refrigeration system. The lamp uses a light-emitting diode as a light source rather than conventional UV-emitting light sources. Consequently, the lamp operates with low power drain, at reduced temperatures and has an extremely long life expectancy as compared to conventional detection lamps equipped with incandescent bulbs.